In the solvent extraction process a liquid to be treated is thoroughly mixed with an appropriate other liquid to achieve mass transfer of constituents from the liquid being treated to the other liquid, this being followed by the physical separation of the two liquids.
For practical and efficient operation it is desirable to employ a number of inter-connected contactors, termed a cascade, and preferably a cascade is arranged to provide a counter-current contact between the two liquids or phases.
To obtain a counter-current cascade it is necessary for one liquid (the minority phase) to flow against the pressure gradient created by the other liquid (the majority phase). This can be achieved using fluidic flow devices in the form of jet pumps.
A jet pump is a three port device in which an inlet or drive flow at a first port passes through a nozzle or jet to enter a co-axial diffuser section spaced from the nozzle or jet and forming an outlet port. A third port communicates with the interspace between the nozzle and diffuser with the result that flow therefrom is entrained in the flow from the nozzle to the diffuser.
It is known to arrange contactors in a countercurrent mode and to include intervening jet pumps between the contactors to assist in the counter-current flows through the cascade. As example, reference is made to U.S. Pat. Specification 4,693,822. In FIG. 5 of the reference, which discloses a cascade of four contactors, the same liquid that is the aqueous flow or the organic flow is not applied to the drive port of each jet pump in the cascade. A change-over occurs at the centre of the cascade as shown in FIG. 5 of the reference.